Go during school lecture (6)
I believe the answer is:
speech
'lecture' is the definition.
(synonyms)
'go during school' is the wordplay.
'go' becomes 'pee' (both can mean to urinate).
'during' indicates putting letters inside.
'school' becomes 'sch'.
'pee' inserted into 'sch' is 'SPEECH'.
(Other definitions for speech that I've seen before include "Giving address" , "Formal address or discourse" , "Formal spoken communication delivered to an audience" , "Vocal communication" , "The business of talking" .)